Organic solvents are compounds that can be used to dissolve, soften, melt, or extract another compound, such as grease, soil, oil, paint, glue, stains, etc., and, therefore, are commonly used in cleaning formulations. Typical organic solvents include aliphatic hydrocarbons, isoparaffins, aromatic hydrocarbons, chlorinated hydrocarbons, terpenes and d-limonene, among others. Unfortunately, many organic solvents have limited solubility, or practically zero solubility, in water which severely limits the amounts that can be added to water-based cleaning formulations sometimes to the point where their beneficial effects cannot be realized.
Coupling agents are compounds that facilitate dissolution and dispersion of organic solvents, into water-based formulations, in greater amounts than otherwise possible, while the formulations retain their clarity, viscosity and homogeneity. Various coupling agents are known for use in cleaning formulations including propylene glycol, diethylene glycol, glycol ethers, and surfactants, among others. See U.S. Pat. Nos. 4,511,488. However, lower glycol ethers are volatile organic compounds (VOCs) which are environmentally undesirable. Some higher glycol ethers have lesser solubility in water-based systems, which limits their utility as coupling agents.
Esters of levulinic acid are well known and described in the art as plasticizers and solvents. For example, GB423919 describes the production of esters of levulinic acid with modified polyhydric alcohols which are useful as plasticizers for cellulose derivatives in coating applications.
For example, U.S. Pat. No. 2,654,723 describes the preparation of diethylene glycol dilevulinate by heating a mixture of levulinic acid and diethylene glycol, in a solvent such as toluene and in the presence of an acid catalyst.
International Patent Application No. WO 2010/102203 describes the preparation of alkyl levulinates by an acid-catalyzed reaction of furfuryl alcohol with other alcohols including methanol, ethanol, propanol, isopropanol, butanol, and isobutanol.
In U.S. Pat. No. 3,203,964, a process is described for manufacturing levulinic acid esters by heating furfuryl alcohol with another alcohol selected from the group consisting of unsubstituted primary and secondary carbon chain and oxygen-carbon chain aliphatic and carbon ring and oxygen-carbon ring cycloaliphatic alcohols containing from 1 to 10 carbon atoms, in the presence of a an acid catalyst. U.S. Pat. No. 3,203,964 states that the levulinic acid esters are useful as plasticizers or solvents.
International Patent Application Publication No. WO2007/094922 describes the use of ester derivatives of levulinic acid to replace traditional plasticizers and coalescent solvents in polymer compositions, plastics and water-based coatings, thereby to lowering their VOC content.
GB478854 describes the use of lower alkylene glycol dilevulinates (e.g., dilevulinates of propylene glycol, diethylene glycol, ethylene glycol, trimethylene glycol (1,3-propanediol), 1,3-butylene glycol and dimethyl-dimethylol) as suitable high boiling softening agents for cellulosic pellicles. U.S. Pat. No. 2,581,008 discloses the preparation of dilevulinates of mono-, di- and tri-ethoxylated diols and their use as plasticizers for polyvinyl acetals and other polymers.
Furfuryl alcohol and levulinic acid are two of the reactants that can be used to manufacture esters of levulinic acid, e.g., alkylene glycol dilevulinates. They are both inexpensive renewable feedstocks available from biomass. Thus, the use of levulinates as solvents in water-based cleaning formulations would be economically and environmentally beneficial.
A solvent which would facilitate the use of organic solvents having low water solubility in water-based systems, such as aqueous cleaning formulations, would provide significant advantages relative to solvents traditionally used as coupling agents. The present invention provides for the use of alkylene glycol dilevulinates as new alternative coupling agent solvents in water-based formulations.